In vehicular applications, a typical four-wheel steering system steers the front and the rear wheels of a vehicle. More specifically, a rear wheel steering portion of the system may produce a desired rear wheel steering angle to improve directional stability at high speeds and maneuverability at low speeds. The high-speed steering method may reduce vehicle yaw by steering the front and rear wheels in the same direction, or in phase, and thereby improve vehicle safety. The low speed steering method may achieve tight turning radii at low speeds by steering the front and rear wheels in different directions, or out of phase, to thereby reduce the effective turning radius of the vehicle.
In the rear wheel steering portion of a four-wheel steering system, an electric motor is typically employed to steer the rear wheels. Attempting to turn the rear wheels when the vehicle is substantially stopped, or when the steered wheels are otherwise static and not rolling, places high torque loads on the electric motor. Achieving high torque loads mandates utilization of larger motors, requiring larger size and weight, and may result in less precise control.
The above described and other features are exemplified by the following Figures and Description in which a vehicular system is disclosed that includes a controller and an electric motor in signal communication with the controller for receiving current and rotating at speed; while the controller implements a method for controlling the rear steering angle of a vehicle that includes calibrating a static vehicle speed threshold, detecting an actual vehicle speed below the calibrated static vehicle speed threshold, determining whether the phase of a rear steering angle is correct in response to the detected speed below threshold, ramping to zero the rear steering angle if the determined phase is not correct, deciding whether the rear steering angle is greater than a desired rear steering angle if the determined phase is correct, and ramping down the rear steering angle to the desired rear steering angle in response to the decidedly greater angle by commanding an electric motor operably coupled to the steering rack.